Electrooptical device and method of fabricating the same

ABSTRACT

There is disclosed an electrooptical device capable of achieving a large area display by making full use of the size of the substrate. An active matrix substrate acts as a driver portion for the reflection-type electrooptical device. A pixel matrix circuit and logic circuitry are formed on the active matrix substrate. At this time, the logic circuitry is disposed, by making use of a dead space in the pixel matrix circuit. The area occupied by the pixel matrix circuit, or image display region, can be enlarged without being limited by the area occupied by the logic circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 10/079,766, filed on Feb. 19, 2002 now U.S. Pat. No. 6,765,562, nowallowed, which is a continuation application of U.S. application Ser.No. 08/937,377, filed on Sep. 25, 1997, now U.S. Pat. No. 6,384,818 B1,which claims the benefit of a foreign priority application filed inJapan on Sep. 27, 1996, as Serial No. 08-277486. This application claimspriority to all of these applications, and all of these applications areincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrooptical device having drivercircuits consisting of semiconductor devices making use of thin-filmsemiconductors and also to a method of fabricating such anelectrooptical device. More particularly, the invention relates to anactive matrix electrooptical device (AMEOD) where a pixel matrix circuitand logic circuitry are integrated on the same panel.

2. Description of the Related Art

In recent years, techniques for fabricating thin-film transistors (TFTs)on an inexpensive substrate have evolved rapidly, because there is anincreasing demand for active matrix electrooptical devices. In an activematrix electrooptical device, millions of pixels are arranged in rowsand columns. TFTs are arranged at each pixel. Electric charge going intoand out of each pixel electrode is controlled by the switching action ofeach TFT.

Electrooptical devices include liquid crystal displays making use ofoptical characteristics of liquid crystals, electroluminescent displaysemploying electroluminescent materials typified by ZnS:Mn, andelectrochromic displays exploiting the color changing characteristics ofelectrochromic materials.

These electrooptical devices are active devices that can bematrix-addressed. High-definition display can be accomplished byutilizing this active matrix construction. As mentioned above, a greatfeature of the active matrix construction lies in that electric chargegoing into and out of pixel electrodes arranged in rows and columnswithin an image display region of an electrooptical device is controlledby turning on and off pixel electrodes disposed at the pixels.

Another feature of the active matrix construction is that drivercircuits for driving pixel TFTs are necessary to control pixels. In theprior art technique, a pixel matrix circuit formed on a glass substratehas been connected with a separately prepared driver IC to form anactive matrix circuit.

In recent years, however, it has become common practice to form pluralcircuit TFTs forming driver circuits and a pixel matrix circuit on thesame substrate to build driver circuits (known as peripheral drivercircuits) around the pixel matrix circuit.

More recently, a system-on-panel (SOP) structure has attracted attentioncomprising a substrate on which control circuits (e.g., a processorcircuit, memory circuits, A/D or D/A converter circuits, correctingcircuits, and a pulse-generating circuit) are formed, as well as drivercircuits (such as shift register circuits or buffer circuits) fordriving pixel TFTs.

A general construction of an electrooptical device is shown in FIG. 3,which gives an example of active matrix liquid crystal display. A pixelmatrix circuit 302 is formed on a glass substrate 301. This pixel matrixcircuit 302 consists of integrated pixel regions. A portion of the pixelmatrix circuit 302 is shown on an expanded scale at 303, where pluralregions (two regions in this example) are arranged in rows and columns.At least one pair of pixel TFT/pixel electrode is disposed in each pixelregion.

A horizontal scanning driver circuit 304 for transmitting data signalsto data lines comprises shift register circuits, level-shiftingcircuits, buffer circuits, and sampling circuits. The level-shiftingcircuits amplify driving voltages.

It is assumed that a shift register circuit is operated with 10 V andthat a buffer circuit is operated with 16 V. In this case, it isnecessary to convert the voltages into other values by a level-shiftingcircuit. Sometimes, a shift register circuit may be constructed bycombining a counter circuit with a decoder circuit. A vertical scanningdriver circuit 305 for transmitting gate signals to gate lines comprisesa shift register circuit, a level-shifting circuit, and a buffercircuit.

It is expected that a control circuit 306 will be located in theposition shown in FIG. 3 in near future. Since the control circuit 306is composed of complex logic circuitry or memory circuitry such as aprocessor occupying a large area, it is expected that the total areaoccupied will increase.

As described above, the pixel matrix circuit 302, the horizontalscanning driver circuit 304, the vertical scanning driver circuit 305,and the control circuit 306 are generally disposed on one glasssubstrate 301. Accordingly, in order to secure a maximum display area ona given size of glass, it is necessary to minimize the area occupied bycircuits other than the pixel matrix circuit.

However, even if the marginal structure as shown in FIG. 3 is adopted,limitations are imposed on increases of the device density of theperipheral driver circuits. Where other values or advantages are addedlike a control circuit, it is more difficult to increase the area of thepixel matrix circuit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electroopticaldevice, or an optical display device, in which a pixel matrix circuitproviding display regions is maximized in area by solving the foregoingproblems to thereby accomplish a large area display making full use ofthe size of the substrate.

An electrooptical device in accordance with the present inventioncomprises a pixel matrix circuit and logic circuitry formed on the samesubstrate. The pixel matrix circuit occupies regions in which the logiccircuitry is fully or partially disposed.

The present invention also provides an electrooptical device comprisingan active matrix substrate having a pixel matrix circuit and logiccircuitry thereon. A liquid crystal material layer is held on the activematrix substrate. The pixel matrix circuit occupies regions in which thelogic circuitry is fully or partially disposed.

A gist of the present invention lies in an electrooptical deviceoperating in the reflective mode or in the emissive mode. This device ischaracterized in that pixel regions located on the rear side of thepixel electrodes are effectively utilized. That is, the logic circuitrywhich would have heretofore been disposed in an outside frame of thepixel matrix circuit as shown in FIG. 3 is totally or partially builtinto the pixel matrix circuit, by making use of the pixel regions.

A cross section is taken through the active matrix construction on whichthe pixel matrix circuit is integrated with the logic circuitry. In thiscross section, the logic circuitry is fully or partially located belowthe pixel electrodes connected with the pixel TFTs forming the pixelmatrix circuit.

The logic circuitry means circuits other than the pixel matrix circuitconsisting of driver circuits and/or control circuits. The controlcircuits embrace every information-processing circuit necessary to drivean electrooptical device, and are typified by processor circuit, memorycircuit, A/D or D/A converter circuit, correcting circuit, apulse-generating circuit.

Since an electrooptical device operated in the reflective mode(typically, a reflective-type liquid crystal display) does not need totransmit light, it is not necessary to make the pixel electrodestransparent to secure optical paths, unlike the transmissive-type liquidcrystal display. Therefore, the rear side of the pixel electrodes (thelower side in the cross section described above) which has beenheretofore impossible for the transmissive-type liquid crystal displayto utilize can be effectively exploited to dispose the logic circuitry.

The reflective-type liquid crystal display operating in theaforementioned reflective mode is next described briefly by referring toFIGS. 4(A) and 4(B). Shown in FIG. 4(A) are an active matrix substrate401, a counter substrate 402, and a liquid crystal material layer 403.Pixel electrodes 404 are formed on top of the active matrix substrate401. If necessary, a reflecting plate may be formed. The pixelelectrodes 404 are protected by a protective film 405.

FIG. 4(A) shows the state in which a TFT is OFF. That is, liquid crystalmolecules are oriented in such a way that they do not vary the directionof polarization of incident light. Under this condition, an arbitrarydirection (in this example, the direction of reflection by a beamsplitter 408) of polarization is given to light 407 by a polarizer 406.The light 407 is caused to enter the liquid crystal material layer 403via the beam splitter 408, which either transmits or reflects the light,depending on the direction of polarization.

As described above, under the condition of FIG. 4(A) (i.e., the TFT isOFF), the light 407 incident on the liquid crystal material layer 403 isreflected by the pixel electrodes 404 such that the direction ofpolarization is not changed. Then, the light reaches the beam splitter408. That is, the light 407 reflected by the pixel electrodes 404 isreturned with the same direction of polarization as the direction ofpolarization of the incident light. Therefore, the light 407 hitting thebeam splitter 408 is reflected and thus does not reach the observer'seye.

On the other hand, FIG. 4(B) shows the state in which the TFT is ON. Theliquid crystal molecules are oriented so as to polarize light 409indicated by one arrow. The light 409 reflected by the beam splitter 408undergoes a change in the direction of polarization by a liquid crystalmaterial layer 410. Then, the light 409 is transmitted through the beamsplitter 408 and reaches the observer's eye.

In this way, the electrooptical device operating in the reflective modeturns on and off light according to whether the TFT is ON or OFF. Thereflection-type liquid crystal display is a typical example of such anelectrooptical device. Furthermore, electrooptical devices areclassified in terms of mode of operation, such as ECB (electricallycontrolled birefringence effect) mode, PCGH (phase change guest-host)mode, OCB mode, HAN (hybrid alignment nematic) mode, and PDLC guest-hostmode (see “LCD Intelligence,” August, pp. 51–63, 1996).

However, the present invention can be applied to any type of operationmode as long as a specularly reflecting plate is disposed immediatelybehind the liquid crystal material layer. Furthermore, the invention canbe applied to active matrix electroluminescent displays operating in theemissive mode and to active matrix electrochromic displays exploitingthe color changing characteristics of electrochromic materials. That is,the invention can be applied to any kind of structure excluding thetransmission-type electrooptical device.

The electrooptical device referred to herein is not limited to aso-called display panel. Rather, the electrooptical device embracescommercial products incorporating display panels. We define theelectrooptical device as every device that performs its intrinsicfunction by electrical action, optical action, or a combination thereof.For the sake of illustration, the “electrooptical device” may refereither to a display panel or to a final product employing such a displaypanel.

The present invention also provides a method of fabricating anelectrooptical device having a pixel matrix circuit and logic circuitryformed on the same substrate. This method is characterized in that thelogic circuitry is totally or partially disposed in regions occupied bythe pixel matrix circuit.

The invention also provides another method of fabricating anelectrooptical device. This method starts with forming an active matrixsubstrate having a pixel matrix circuit and logic circuitry on the samesubstrate. Then, a liquid crystal material layer is formed and held onthe active matrix substrate. This method is characterized in that thelogic circuitry is totally or partially disposed in regions occupied bythe pixel matrix circuit.

An electrooptical device in accordance with the present invention isschematically shown in FIG. 5, where a pixel matrix circuit 502 isintegrated with logic circuitry, 503 and 504, on a glass substrate 501.The logic circuitry includes driver circuits and control circuits. Thelogic circuitry, 503 and 504, overlaps the pixel matrix circuit 502.

This configuration cannot be accomplished by a transmission-typeelectrooptical device that needs to secure an optical path or openingfor passing backlight, for the following reason. Major portions of thepixel matrix circuit of the transmission-type electrooptical device areopenings and so it is impossible to build the logic circuitry into thepixel matrix circuit without decreasing the amount of light transmitted.

Accordingly, it can be said that the present invention is a techniquecapable of being embodied in a reflection-type electrooptical devicewithout the need to secure an optical path. In particular, the logiccircuitry is formed below (on the rear side of) the pixel electrodesacting as a reflective plate.

In FIG. 2(A), conductive interconnects, 146–150, act to interconnectcircuit TFTs comprising first, second, . . . , the Nth circuit TFTs,thus constructing A/D converters, memory circuits, and so on. Thus, thelogic circuitry is completed.

Data lines 152–155 are provided to permit data signals to go into andout of first and second pixel TFTs. It can be said that the data lines153 and 155 are extraction electrodes for pixel electrodes 160 and 161.The surfaces of these pixel electrodes 160 and 161 are kept specularsuch that they act as reflective plates for reflecting incident light.If necessary, a reflective film serving as a mirror may be formed overthe pixel electrodes 160 and 161.

The structure described thus far enables the logic circuitry, 503 and504, to be incorporated in the pixel regions forming the pixel matrixcircuit 502, as shown in FIG. 5.

Other objects and features of the invention will appear in the course ofthe description thereof, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A)–1(D), 2(A)–2(C) are cross-sectional views illustrating aprocess sequence for fabricating TFTs in accordance with the invention;

FIG. 3 is a perspective view of an electrooptical device in accordancewith the invention;

FIGS. 4(A) and 4(B) are views illustrating the operation of areflection-type liquid crystal display;

FIG. 5 is a perspective view of an electrooptical device in accordancewith the invention;

FIGS. 6(A)–6(C) are top plan views of another electrooptical device inaccordance with the invention;

FIGS. 7(A) and 7(B) are top plan views of a further electroopticaldevice in accordance with the invention;

FIGS. 8(A) and 8(B) are cross-sectional views of a still otherelectrooptical device in accordance with the invention;

FIGS. 9(A) and 9(B) are cross-sectional views of a yet otherelectrooptical device in accordance with the invention; and

FIGS. 10(A)–10(F) are views illustrating commercial products employingelectrooptical devices in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

A process sequence for fabricating an active matrix substrate having astructure in accordance with the present invention is now described byreferring to FIGS. 1(A)–1(D) and 2(A)–2(C). It is to be noted that thepresent embodiment represents one example of the present invention andthat the process conditions such as numerical values given below may beappropriately determined by the manufacturer.

First, a substrate 101 having an insulating surface is prepared. In thepresent embodiment, a glass substrate on which a film of silicon oxideis deposited is used as the substrate 101. Instead of the glasssubstrate, a quartz substrate may be used.

Then, an amorphous silicon film (not shown) is formed to a thickness of500 Å. The amorphous silicon film is converted into a crystallinesilicon film by an appropriate crystallization technique. Thecrystallization is carried out by heat treatment or laser processing orboth. Where the heat treatment is made, it is necessary to determine thecrystallization temperature, taking account of the maximum processingtemperature of the substrate of glass or quartz.

After obtaining the crystalline silicon film (not shown), it ispatterned to form islands of an active layer, 102–105. The island ofactive layer 102 forms a first pixel TFT, while the island of activelayer 105 forms a second pixel TFT.

First through Nth circuit TFTs (the intermediate circuit TFTs are notshown) are disposed between the first and second pixel TFTs which areboth P-channel TFTs. The island of active layer 103 forms a firstcircuit TFT, whereas the island of active layer 104 forms an Nth circuitTFT. In the present embodiment, the first circuit TFT is of theN-channel type, whereas the Nth circuit TFT is of the P-channel type.

The number, or N, of circuit TFTs required varies according to theconstruction of the logic circuitry. In practice, millions of pixel TFTsare arranged in rows and columns on the glass substrate 101. The circuitTFTs form the logic circuitry among these pixel TFTs.

Of course, the first circuit TFT is not always identical in structurewith the Nth circuit TFT. In the description of the present embodiment,it is assumed that they are fundamentally identical in structure.Obviously, the structure is varied by the logic circuitry parameterssuch as the channel length and the presence or absence of offsetregions.

After forming the islands of the active layer, 102–105, a gate insulatorfilm 106 is deposited to a thickness of 1200 Å. This gate insulator film106 may be formed from silicon oxide by plasma CVD or LPCVD. Of course,thermal oxidation may also be utilized.

Then, a patterned layer, 107–110, consisting mainly of aluminum isformed on the gate insulator film 106. In the present embodiment, thepatterned layer, 107–110, is made of an aluminum film having a thicknessof 4000 Å and containing 0.2% by weight of scandium. The scandium iseffective in preventing generation of hillocks and whiskers on thealuminum film.

The patterned layer, 107–110, provides a prototype for gateelectrodes/interconnects formed later. The material of this patternedlayer can also be tantalum, niobium, molybdenum, or other metallicmaterial, as well as aluminum. Furthermore, the patterned layer can be acrystalline silicon film, or polysilicon film, to which conductivity hasbeen imparted.

In this way, a state shown in FIG. 1(A) is obtained. A resist mask (notshown) is left on the patterned aluminum layer, 107–110. Then, anodicoxidation is carried out, using a 3% aqueous solution of tartaric acidas an electrolyte. As a result, a porous anodic oxide film, 111–114, isformed. In the present embodiment, the current is increased up to 2 to 3mA. The voltage is increased up to 8 V. The anodic oxide film is grownto a thickness of 0.7 μm.

At this time, the anodic oxidation reaction progresses parallel to thesubstrate, because the resist mask (not shown) remaining on top of thepatterned aluminum layer, 107–110, inhibits the reaction.

After removing the resist mask with a proprietary stripping solution,anodic oxidation is again performed to form a dense and firm anodicoxidation film, 115–118, having a thickness of 1000 Å. The usedelectrolyte is prepared by neutralizing an ethylene glycol solutioncontaining a 3% tartaric acid with aqueous ammonia to adjust the pH to6.92. The film is treated with a current that is increased up to 5 to 6mA. The voltage is increased up to 100 V.

Since the electrolyte intrudes into the porous anodic oxidation film,111–114, the anodic oxidation film, 115–118, is shaped as shown in FIG.1(B). At the same time, gate electrodes 119–122 for controlling theoperation of the first, second pixel TFTs and first, Nth circuit TFTsare defined (FIG. 1(B)).

Because the anodic oxidation film, 115–118, is dense and firm, itprotects the gate electrodes 119–122 from being damaged during laterprocess steps and shields these gate electrodes against heat producedduring the later process steps.

After obtaining the state shown in FIG. 1(B), the gate insulator film106 is selectively etched off by a self-aligned dry etching process,using the gate electrodes 119–122 and the porous anodic oxide film,111–114, as a mask. As a result, the gate insulator film 106 is leftbehind only under the gate electrodes and the porous anodic oxide film.

Subsequently, the porous anodic oxide film, 111–114, is removed. Thoseregions which will become P-channel TFTs (i.e., the regions becoming thefirst, second pixel TFTs, and the Nth circuit TFT) are coated with aresist mask 123.

Then, P (phosphorus) ions for imparting N type to the island of activelayer 103 are implanted into this layer at a high accelerating voltageof about 80 kV by ion implantation techniques. Since the acceleratingvoltage is high, every P ion is implanted into the island of activelayer 103 across the remaining gate insulator film 106.

Thereafter, second ion implantation is performed at a decreasedaccelerating voltage of approximately 10 kV. Since the acceleratingvoltage is low, the P ions are not implanted under the remainingportions of the gate insulator film 106.

The second P ion implantation creates a source region 124 and a drainregion 125 for the first circuit TFT. Those regions which are implantedwith the P ions through the gate insulator film 106 become regions 126and 127 more lightly doped than the source/drain regions 124, 125.Especially, the lightly doped region 127 formed closer to the drainregion 125 is known as a lightly doped drain (LDD) region andeffectively suppresses off currents and leakage currents.

An intrinsic or substantially intrinsic channel formation region 128 notimplanted with P ions is formed immediately under the gate electrode120. Strictly, both ends of the channel formation region 128 locatedimmediately under the anodic oxide film 116 act as offset regions towhich no gate voltage is applied.

In this way, a state shown in FIG. 1(C) is obtained. The resist mask 123is removed, and then regions becoming N-channel TFTs are coated with aresist mask 129. Boron (B) ions are implanted into the islands of anactive layer, 102, 104, and 105, to impart P type.

In the same way as in the case of the N-channel TFTs, the first ionimplantation is effected at a higher accelerating voltage, and thesecond ion implantation is done at a lower accelerating voltage. As aresult of this implantation of the B ions, source regions 130, 131,drain regions 132, 133, lightly doped regions 134–137, and channelformation regions 138, 139 for the first and second pixel TFTs areformed. Also, a source region 140, a drain region 141, lightly dopedregions 142, 143, and a channel formation region 144 for the Nth circuitTFT are formed.

As a result of these process steps, N- and P-channel TFTs are separatelyformed at an arrangement shown in FIG. 1(D). Since the presentembodiment merely represents one example of the present invention, theN- and P-channel TFTs may be manufactured by methods different from theforegoing.

Then, the dopants implanted in the active layer are activated by a heattreatment, laser processing, or both. Simultaneously with theactivation, the crystallinity of the active layer sustained damage dueto the ion implantation is healed.

After removing the resist mask 129, a first interlayer dielectric film145 is formed to a thickness of 5000 Å. This interlayer dielectric film145 can be made of a silicon oxide film, a silicon nitride film, or alamination film thereof.

Subsequently to the formation of the first interlayer dielectric film145, contact holes are created, and conductive interconnects 146–150 forthe circuit TFTs are formed. These conductive interconnects 146–150 actto interconnect the circuit TFTs. The first through Nth circuit TFTs areinterconnected to build logic circuitry. Under this condition, the firstthrough Nth circuit TFTs are completed.

In this manner, a state shown in FIG. 2(A) is derived. Then, a secondinterlayer dielectric film 151 is formed to a thickness of 1 μm frompolyimide that is an organic resinous material which transmits light.The polyimide can be readily formed into a thick film by spinningtechniques. Also, the polyimide has excellent planarity. Furthermore,the parasitic capacitance can be reduced, because its relativedielectric constant is small.

Then, data lines 152–155 connected with the first and second pixel TFTsare formed. The data lines 152, 154 connected with the source regions130, 131 transmit data signals from driver circuits and the data lines153, 155 connected with the drain regions 132, 133 serve as pipelinesfor connecting pixel electrodes (formed later) with the TFTs.

After forming the data lines 152–155, a third interlayer dielectric film156 is formed to a thickness of 5000 Å. In the present embodiment, thethird interlayer dielectric film 156 is also made of polyimide (FIG.2(B)).

Thereafter, a black matrix, 157 and 158, is formed, using a materialthat functions to absorb light. In the present embodiment, a resinousmaterial in which black dye or pigment has been dispersed is used.Titanium nitride or the like may also be used. The resinous material maybe selected from acrylic-based materials, polyimide, polyimidamide, andpolyamide.

After forming the black matrix, 157 and 158, a fourth interlayerdielectric film 159 is formed from polyimide-to a thickness of 3000 Å onthe black matrix. The fourth interlayer dielectric film 159 may also bemade of silicon oxide, or a silicide such as silicon nitride.

Notice that pixel electrodes, or a reflective plate, on the fourthinterlayer dielectric film 159 need to be formed on a sufficientlyplanarized surface that reflects light precisely. Therefore, it isimportant that the fourth interlayer dielectric film 159 be sufficientlyflat.

Then, pixel electrodes 160 and 161 are formed on the fourth interlayerdielectric film 159. The pixel electrodes 160 and 161 may be made of ametallic material. To set up a uniform electric field over the wholesurface, the material preferably consists principally of aluminum of lowresistivity. Also, in order to reflect incident light effectively, thesurface of the pixel electrodes 160 and 161 is preferably made specular.

As shown in FIG. 2(C), the black matrix, 157 and 158, is patterned so asto fill the gaps between the pixel electrodes 160 and 161. As can beseen from FIG. 2(C), the first through Nth circuit TFTs are arrangedbelow the pixel electrode 160, thus forming logic circuitry.

Normally, a protective film is formed over the pixel electrodes 160 and161 to prevent them from deteriorating. Where the pixel electrodes 160and 161 cannot act as a reflective plate, a separate thin metal can beformed as a reflective plate.

In this way, an active matrix substrate as shown in FIG. 2(C) can bemanufactured in the manner described thus far. In the presentembodiment, the transistors are planar-type transistors. The presentinvention can also be easily applied to other structures of TFTs such asthe staggered type and inverted-staggered type.

An active matrix liquid crystal display can be built by sandwiching aliquid crystal material between the active matrix substrate manufacturedin the present embodiment and a counter substrate. Where anelectroluminescent material is inserted as a light-emitting layerinstead of the liquid crystal material layer, an active matrixelectroluminescent display can be fabricated. Where a solutioncontaining an electrochromic colorant, dye, or electrolyte is inserted,an active matrix EC display is manufactured.

A guest-host liquid crystal display can be manufactured, for example,using a host liquid crystal material to which dichroic dye is added. Thecell may be assembled by a well-known method and so the assemblyoperation is not described herein. Among guest-host types, the PCGH(phase change guest-host) type needs no polarizers and thus accomplisheshigh contrast and bright display.

Besides the guest-host type, ECB (electrically controlled birefringence)effect mode and PDLC (polymer dispersed liquid crystal) mode can beused. These types of device require neither color filters nor polarizersand therefore are quite advantageous for the reflection type liquidcrystal display that tends to suffer from large light loss. In the caseof the PDLC mode, a liquid crystal panel can be built, using only anactive matrix substrate.

Where an electrooptical device is constructed in accordance with thepresent invention, the active matrix substrate and counter substrate arepreferably made of glass or quartz. If a silicon wafer or the like isused to manufacture the active matrix substrate, the finishedelectrooptical device might deform due to a stress. In the worst case,the device might be damaged.

The greatest feature of the present invention is that circuit TFTs areformed under the pixel electrodes 160 and 161, as shown in FIG. 2(C).This construction has been impossible to achieve by thetransmission-type electrooptical device that transmits light.

More specifically, regions under the pixel electrodes must be keptunfilled to form an optical path for the transmission-typeelectrooptical device, however, in the case of the reflection type andemissive type of electrooptical devices in the present invention, drivercircuits and logic circuitry including control circuits can be packed inthese regions under the pixel electrodes.

Accordingly, in the present invention, the driver circuits and controlcircuits which have been urged to be located in peripheral regions of apixel matrix circuit can be incorporated in regions where the pixelmatrix circuit is disposed. Hence, the pixel matrix circuit on which animage is displayed can be expanded by making full use of the size of theglass substrate.

In recent years, transmission-type electrooptical devices tend to havegradually increasing aperture ratios. This means that the unfilled areain which logic circuitry can be packed in accordance with the presentinvention is increased. This tendency will become more conspicuous assemiconductor devices decrease in size rapidly. Hence, it can beconsidered that the importance of the present invention is enhancedfurther.

As can be understood from the fundamental structure of the presentinvention, any contrivance can be made according to the need of thedesigner or manufacturer of the electrooptical device. That is, theinventive concept lies in that “logic circuitry is built in regionswhere a pixel matrix circuit is disposed.” The designer mayappropriately determine how the logic circuitry is arranged.

The configuration of an electrooptical device fabricated in accordancewith the present embodiment is next described by referring to FIG. 5 inwhich a glass substrate 501 and a pixel matrix circuit 502 are shown.Where a part of the pixel matrix circuit 502 is enlarged, it can be seenthat logic circuits 503 and 504 are incorporated in a pixel region. Itis to be noted that this construction comprising the two logic circuits503 and 504 incorporated in one pixel region merely represent oneexample. One functional circuit can be fabricated over plural pixelregions by making connections with other pixel regions by means ofconductive interconnects.

Where the logic circuit 504 is enlarged, it can be observed that acircuit 505 is constructed. For example, the left portion of the circuit505 is a CMOS circuit, while the right portion is a NAND (or NOR)circuit.

The logic circuitry can be built into the pixel matrix circuit by thestructure described thus far. That is, the pixel matrix circuit 502 canbe constructed by making full use of the size of the glass substrate501, as shown in FIG. 5.

In the reflection-type electrooptical device to which the invention isapplied, the pixel matrix circuit forms an image display region as itis. Therefore, large area display can be accomplished such that nolimitations are imposed on the position at which the logic circuitry islocated.

Embodiment 2

In the present embodiment, the usefulness of the circuit designaccording to the present invention is described. The invention ischaracterized in that a pixel matrix circuit and logic circuitry can bepositioned in the same regions on a substrate of glass or quartz.

FIG. 6(A) shows one device in accordance with the present invention.This device has a glass substrate 601 on which a driver circuit 602 anda control circuit 603 are formed by the process sequence ofEmbodiment 1. Strictly, a driver circuit can be disposed in the region602, and a control circuit can be disposed in the region 603.

The driver circuit 602, the control circuit 603, and so on constitutelogic circuitry. This logic circuitry and a pixel matrix circuit 604 arearranged in the same regions. Practically, pixel TFTs forming the pixelmatrix circuit 604 and circuit TFTs are formed in the same layer. Pixelelectrodes connected with the pixel TFTs overlap the circuit TFTs (FIG.2(C)).

Therefore, in FIG. 6(A), the regions of the logic circuitry whichoverlap the pixel matrix circuit 604 are indicated by the broken lines.Where the active matrix substrate is viewed from above as shown in FIG.6(A), only the pixel electrodes are seen; the underlying logic circuitryis invisible.

In the case of FIG. 6(A), a vertical scanning driver circuit (thevertical portion of the T-shaped driver circuit 602) is disposed in thecenter of the pixel matrix circuit 604. No limitations are imposed onthe method of scanning signals. Ordinary methods can be used. Besides,the gate signal-transmitting system of the left portion of the substratemay be different from the gate signal-transmitting system of the rightportion. The left and right portions are located on opposite sides ofthe vertical scanning driver circuit, for example.

FIG. 6(B) shows a further device in accordance with the presentinvention. Diver circuits 605 are located at ends of a glass substrate601. Control circuits 606–608 are arranged in a central unfilled space.It is expected that control circuits will require relatively large areasbecause they are complex in configuration. Therefore, the structure ofFIG. 6(B) gives increased degrees of freedom in designing the controlcircuits 606–608, thus producing favorable results.

In FIG. 6(B), the control circuits 606, 607, and 608 are shown to bearranged in three separate regions and divided into blocks simply interms of functions. It is not always necessary to divide these controlcircuits into different blocks.

In the example of FIG. 6(B), the driver circuits 605 are incorporated inthe pixel matrix circuit 604. Instead, only the driver circuits 605 maybe placed outside the pixel matrix circuit 604. This will increase thedegrees of freedom in designing the control circuits 606–608.

FIG. 6(C) shows a further device in accordance with the presentinvention. A driver circuit 609 is shaped like a crisscross. The surfaceof a substrate is divided into four regions. Control circuits 610–613are arranged in these four regions, respectively.

No restrictions are imposed on the method of driving the configurationof FIG. 6(C). The four regions may be driven as a unit. Also, the fourregions may be driven by separate systems. In some cases, four differentframes of image may be displayed on the single substrate.

Embodiment 3

The present embodiment represents one example in which effective use ofthe pixel regions is made in practicing the present invention. Themethod of arranging the pixel electrodes is next described in detail.

In FIG. 7(A), data lines 701–704 are arranged in parallel. Gate lines705–707 are arranged in parallel to each other and intersect the datalines 701–704 at right angles. Pixel TFTs are connected with theintersections of the gate lines 705 and the data lines 701–704.Similarly, pixel TFTs are connected with the intersections of the gatelines 706, 707 and the data lines 701–704.

In the structure shown in FIG. 7(A), two sets of pixel TFTs and pixelelectrodes (indicated by the broken lines 708 and 709) are arranged inone pixel region that is surrounded, for example, by the gate lines 705,706 and data lines 702, 703. This structure permits the area of onepixel region to be approximately doubled compared with the prior artstructure in which one set of pixel TFT and pixel electrode is arrangedin one pixel region. More specifically, when logic circuitry 710(hatched region) is incorporated in pixel regions, the logic circuitrycrosses the data lines at fewer locations, thus reducing breaks in metallines.

In FIG. 7(B), data lines 711–714 are arranged in parallel. Gate lines715–718 are arranged in parallel to each other and intersect the datalines 711–714 perpendicularly. Pixel TFTs are connected with theintersections of the gate lines 715 and the data lines 711–714.Similarly, pixel TFTs are connected with the intersections of the gatelines 716–718 and the data lines 711–714.

In the structure shown in FIG. 7(B), four sets of pixel TFTs and pixelelectrodes (indicated by the broken lines 719–722) are arranged in onepixel region that is surrounded, for example, by the gate lines 716, 717and data lines 712, 713, unlike the structure of FIG. 7(A). Thisstructure of FIG. 7(B) permits the area of one pixel region to beenlarged further. A region about four times as wide as the region of theprior art device can be secured. In this structure, logic circuitry 723crosses the gate lines and data lines at much reduced locations.Consequently, electrooptical devices can be manufactured with stillhigher yield.

Embodiment 4

In the present embodiment, a structure different from the Embodiment 1of the electrooptical device fabricated in accordance with the presentinvention is given. This structure is similar to the structure ofEmbodiment 1 shown in FIG. 2(C) except for the following points.Therefore, only these points are described, using reference numerals, byreferring to FIGS. 8(A) and 8(B).

The structure shown in FIG. 8(A) comprises pixel TFTs of double gatestructure. That is, two gate electrodes are formed on the active layer.Redundancy for preventing malfunctions of the pixel TFTs can beobtained.

Two gate electrodes 801 and 802 are made of a film of crystallinesilicon. Using these gate electrodes 801 and 802, a source region 803,lightly doped regions 804–807, and a drain region 808 can be formed byion implantation. Especially, the lightly doped regions 805 and 807disposed on the side of the drain region are known as LDD (lightly dopeddrain) regions and are expected to suppress off currents and leakagecurrents effectively.

Referring next to FIG. 8(B), two sets of pixel TFTs and pixel electrodesare inserted between adjacent data lines 809 and 810. This structure isthe same as the structure shown in FIG. 7(A). The data lines 809, 810and pixel electrodes 811, 812 shown in FIG. 8(B) correspond to the datalines 702, 703 and the pixel electrodes 708, 709, respectively, shown inFIG. 7(A).

Another feature of the structure shown in FIG. 8(B) is that the pixelTFTs and circuit TFTs have a salicide structure. For instance, a CMOScircuit (inverter circuit) 813 is formed by two circuit TFTs. In thiscircuit 813, a tungsten silicide layer, 814–816, is formed over thesource region, drain region, and gate electrode to facilitate makingohmic contacts.

The method of forming the silicide structure is well known and so is notdescribed below. In the present embodiment, the silicide structure isformed, using a sidewall 817. Titanium, molybdenum, cobalt, and platinumcan be used as a silicide material for the salicide structure, as wellas tungsten.

Embodiment 5

In the present embodiment, an example in which special functions aregiven to a black matrix structure is described by referring to FIGS.9(A) and 9(B). The structure is roughly identical with the structure ofEmbodiment 1 described in conjunction with FIG. 2(C) and so onlyrequired portions will be described, using reference numerals, byreferring to FIGS. 9(A) and 9(B).

In FIG. 9(A), a black matrix 901 is made of titanium nitride. Sincetitanium nitride exhibits quite small surface reflection, the titaniumnitride functions as a black matrix and as a conductive material. Theblack matrix 901 is laid to overlap pixel electrodes 902. An auxiliarycapacitance is formed between the black matrix and each pixel electrode.A dielectric layer 903, or a fourth interlayer dielectric film, islocated between the black matrix 901 and the layer of the pixelelectrodes 902. The dielectric layer 903 may be made of an organicresinous material such as polyimide, silicon oxide, or silicon nitride.

In the structure of the present embodiment, an area approximating eachpixel region can be used as an auxiliary capacitance and, therefore,sufficient capacitance can be obtained. Accordingly, the material andthe thickness of the fourth interlayer dielectric film 903 should beselected, placing emphasis on the planarizing effect.

In FIG. 9(B), a black matrix 906 fills the space between a pixelelectrode 904 and an adjacent pixel electrode 905. The black matrix 906is made of an organic resinous material in which a black dye has beendispersed.

The structure of FIG. 9(B) is intended to suppress a lateral electricfield that might be produced parallel to the substrate between the pixelelectrodes 904 and 905, thereby preventing disclination lines, ordisturbance in the orientation of the liquid crystal material. For thispurpose, a material having a relative dielectric constant much smallerthan that of the liquid crystal material is used to cover ends(especially corners) of the pixel electrodes 904 and 905. As a result,an electric field produced by the pixel electrodes concentrates in theliquid crystal material having the higher relative dielectric constant,thus suppressing the generation of a lateral electric field between thepixel electrodes.

The liquid crystal material used in the present invention has a relativedielectric constant lying between 3.5 and 10 and shows dielectricanisotropy. When an electric field is applied to the liquid crystalmaterial, the relative dielectric constant is about 10. In contrast, therelative dielectric constant of the organic resinous material formingthe black matrix 906 is approximately 3.0 to 3.5. Thus, the requirementof the present embodiment is satisfied.

If a sufficient film thickness cannot be obtained (i.e., the ability toblock light is insufficient), trenches can be formed in the thirdinterlayer dielectric film 907 before the formation of the black matrix906. In particular, the third interlayer dielectric film 907 is etchedby self-alignment techniques, using the pixel electrodes 904 and 905 asa mask. The black matrix 906 is buried in the trenches, thus obtainingsufficient ability to block light.

The fourth interlayer dielectric film 159 shown in FIG. 2(C) can beomitted and thus the number of interlayer dielectric layers can bereduced by one. This simplifies the fabrication process, which in turnleads to an improvement in the production yield.

Embodiment 6

The present embodiment illustrates some examples of finishedelectrooptical apparatus incorporating an electrooptical device (or,image display device) utilizing the present invention. The image displaydevice may be designed as the direct-view type or as the projectiontype, depending on the need.

Examples of the finished electrooptical apparatus include TV camera,head mounted display, car navigational system, front projection system,rear projection system, video camera, and personal computer. Some simpleexamples of these commercial products are next described by referring toFIGS. 10(A)–10(F).

Referring to FIG. 10(A), there is shown a TV camera. The body of thiscamera is indicated by numeral 2001. This TV camera comprises the body2001, a camera section 2002, a display unit 2003, and operation switches2004. The display unit 2003 is used as a viewfinder.

Referring next to FIG. 10(B), there is shown a head mounted displaywhose body is indicated by numeral 2101. This display comprises tworelatively small display units 2102 and a band 2103, as well as the body2101.

Referring next to FIG. 10(C), there is shown a car navigational system.The body of this system is indicated by numeral 2201. The body 2201includes a display unit 2202 and operation switches 2203. Thenavigational system further includes an antenna 2204. The display unit2202 is used as a monitor. The resolution can be selected from arelatively wide range of values because the main purpose is to displaymaps.

Referring next to FIG. 10(D), there is shown a personal communicationsdevice that is a digital cellular system in the present embodiment. Thebody of this device is indicated by 2301 and has an earpiece 2302, amouthpiece 2303, a display unit 2304, and operation buttons 2305. Anantenna 2306 is attached to the body. It is expected that the displayunit 2304 will be required in the future to act as a TV phone capable ofdisplaying moving pictures.

Referring next to FIG. 10(E), there is shown a video camera. The body ofthis camera is indicated by numeral 2401. This body includes a displayunit 2402, an eyepiece 2403, operation switches 2404, and a tape holder2405. An image taken and displayed on the display unit 2402 can beviewed on a real-time basis through the eyepiece 2403. Hence, the usercan take pictures while watching the image.

Referring to FIG. 10(F), there is shown a front projection system whosebody is indicated by 2501. The body 2501 includes a light source 2502, adisplay unit 2503, and optics 2504 having a beam splitter andpolarizers. The front projection system further has a screen 2505 thatis a large-area screen used for presentations in meetings andannouncements in learned or scientific societies. Therefore, the displayunit 2503 is required to have a high resolution.

The present invention can be applied to various personal communicationsdevices such as rear projection system, mobile computing system, andhandy terminal. In this way, the invention can find quite extensiveapplication and applied to various display media in every application.

It is possible to arrange a pixel matrix circuit and logic circuitry soas to overlap each other in the same regions by carrying out the presentinvention. That is, no limitations are imposed on the area occupied bythe logic circuitry. Therefore, a wide image display region, or pixelmatrix circuit, can be secured by making full use of the size of a glasssubstrate. Also, it follows that the region where the logic circuitrycan be disposed is increased substantially. This increases the number ofdegrees of freedom in designing the electrooptical device. Hence, anelectrooptical device of quite high performance can be accomplished.

1. An active matrix device having a display unit, said display unitcomprising: a substrate having an insulating surface; and a pixel matrixformed over the substrate, said pixel matrix comprising at least firstand second pixels, wherein the first pixel comprises a first thin filmtransistor connected to a first pixel electrode, and a second thin filmtransistor connected to a second pixel electrode, wherein the secondpixel comprises a third thin film transistor connected to a third pixelelectrode, and a fourth thin film transistor connected to a fourth pixelelectrode, and wherein a processor circuit is covered with the firstpixel electrode, the second pixel electrode, the third pixel electrode,and the fourth pixel electrode.
 2. An active matrix device according toclaim 1, wherein said display unit is selected from a reflection-typeliquid crystal display, an active matrix electroluminescence display andan active matrix electrochromic display.
 3. An active matrix deviceaccording to claim 1, wherein said active matrix device is incorporatedinto an article selected from a TV camera, a head mounted display, a carnavigational system, a personal communication device, a video camera anda front projection system.
 4. An active matrix device having a displayunit, said display unit comprising: a substrate having an insulatingsurface; and a pixel matrix formed over the substrate, said pixel matrixcomprising at least first and second pixels, wherein the first pixelcomprises a first thin film transistor connected to a first pixelelectrode, and a second thin film transistor connected to a second pixelelectrode, wherein the second pixel comprises a third thin filmtransistor connected to a third pixel electrode, and a fourth thin filmtransistor connected to a fourth pixel electrode, wherein an A/Dconverter circuit is covered with the first pixel electrode, the secondpixel electrode, the third pixel electrode, and the fourth pixelelectrode.
 5. An active matrix device according to claim 4, wherein saiddisplay unit is selected from a reflection-type liquid crystal display,an active matrix etectroluminescence display and an active matrixelectrochromic display.
 6. An active matrix device according to claim 4,wherein said active matrix device is incorporated into an articleselected from a TV camera, a head mounted display, a car navigationalsystem, a personal communication device, a video camera and a frontprojection system.
 7. An active matrix device having a display unit,said display unit comprising: a substrate having an insulating surface;and a pixel matrix formed over the substrate, said pixel matrixcomprising at least first and second pixels, wherein the first pixelcomprises a first thin film transistor connected to a first pixelelectrode, and a second thin film transistor connected to a second pixelelectrode, wherein the second pixel comprises a third thin filmtransistor connected to a third pixel electrode, and a fourth thin filmtransistor connected to a fourth pixel electrode, and wherein a D/Aconverter circuit is covered with the first pixel electrode, the secondpixel electrode, the third pixel electrode, and the fourth pixelelectrode.
 8. An active matrix device according to claim 7, wherein saiddisplay unit is selected from a reflection-type liquid crystal display,an active matrix electroluminescence display and an active matrixelectrochromic display.
 9. An active matrix device according to claim 7,wherein said active matrix device is incorporated into an articleselected from a TV camera, a head mounted display, a car navigationalsystem, a personal communication device, a video camera and a frontprojection system.
 10. An active matrix device having a display unit,said display unit comprising: a substrate having an insulating surface;and a pixel matrix formed over the substrate, said pixel matrixcomprising at least first and second pixels, wherein the first pixelcomprises a first thin film transistor connected to a first pixelelectrode, and a second thin film transistor connected to a second pixelelectrode, wherein the second pixel comprises a third thin filmtransistor connected to a third pixel electrode, and a fourth thin filmtransistor connected to a fourth pixel electrode, and wherein acorrecting circuit is covered with the first pixel electrode, the secondpixel electrode, the third pixel electrode, and the fourth pixelelectrode.
 11. An active matrix device according to claim 10, whereinsaid display unit is selected from a reflection-type liquid crystaldisplay, an active matrix electroluminescence display and an activematrix electrochromic display.
 12. An active matrix device according toclaim 10, wherein said active matrix device is incorporated into anarticle selected front a TV camera, a head mounted display, a carnavigational system, a personal communication device, video camera and afront projection system.
 13. An active matrix device having a displayunit, said display unit comprising: a substrate havind an insulatingsurface; and a pixel matrix formed over the substrate, said pixel matrixcomprising at least first and second pixels, wherein the first pixelcomprises a first thin film transistor connected to a first pixelelectrode, and a second thin film transistor connected to a second pixelelectrode, wherein the second pixel comprises a third thin filmtransistor connected to a third pixel electrode, and a fourth thin filmtransistor connected to a fourth pixel electrode, and wherein apulse-generating circuit is covered with the first pixel electrode, thesecond pixel electrode, the third pixel electrode, and the fourth pixelelectrode.
 14. An active matrix device according to claim 13, whereinsaid display unit is selected from a reflection-type liquid crystaldisplay, an active matrix electroluminescence display and an activematrix electrochromic display.
 15. An active matrix device according toclaim 13, wherein said active matrix device is incorporated into anarticle selected from a TV camera, a head mounted display, a carnavigational system, a personal communication device, a video camera anda front projection system.